Phenotypic and functional map of myeloid pathways in mouse BM. IL-3Rα expression defines subsets of CMPs and progenitors with prospective potential for erythrocytes (EP), megakaryocytes (MP1 and MP2), or granulocytes and monocytes (GMP). The c-Kit⁺IL-3Rα⁺ population includes the IL-3Rα⁺ CMP subpopulation, GMPs, and the IL-3Rα⁺ megakaryocyte progenitor termed MP2. The c-Kit⁺IL-3Rα^– population includes the IL-3Rα^– CMP subsets, the IL-3Rα^– megakaryocyte progenitor termed MP1, and EPs. The relationship of stem cells and common myeloid and committed myeloid stages to CFU-S, BFU-E, and CFU-E is indicated for each compartment. Despite their major myeloid potential, we also detected a minor level of B-cell progenitor activity in mice given transplants of CMP 3Rα^– or CMP 3Rα⁺ cells. The level of B-cell reconstitution from CMPs was about 10-fold lower when compared to CLPs and about 40-fold lower when compared to HSCs or BM. Phenotypic abbreviations are c-Kit (K), lin (L), and Sca-1 (S).